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Enhancing the methodological framework for inferring selection with ancient DNA: theoretical insights, improvements and comparison

January 15 (Thu) 13:00 - 14:00, 2026

Lucas Sort (Postdoctoral Researcher, Mathematical Genomics RIKEN ECL Research Unit, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Over the past decade, the emergence of ancient DNA has opened new opportunities for studying evolutionary processes. However, inferring signals of selection from such data remains a methodological challenge since controlling for population stratification, admixture, and dynamically changing demographic histories, among other confounding evolutionary processes, is difficult. In this context, ancient DNA time series data, which have proliferated, have led to the development of methods based on two main frameworks: Hidden Markov Models and Generalized Linear Mixed Models. In this work, we aim to clarify how these frameworks relate to the classical Wright–Fisher model, enabling targeted modeling improvements and producing more relevant comparisons across methods.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Measuring evolutionary forces of cultural change

January 13 (Tue) 14:00 - 15:30, 2026

Joshua B. Plotkin (Walter H. and Leonore C. Annenberg Professor of the Natural Sciences, University of Pennsylvania, USA)

I will describe how to measure the forces that drive cultural change, using inference tools from evolutionary theory. We study time series data from large corpora of parsed English texts to identify what drives language change over the course of centuries. We also measure frequency-dependent effects in time series of baby names and purebred dog preferences. The form of frequency dependence we infer helps to explain the diversity distribution of names, and it replicates across the United States, France, Norway and the Netherlands. We find different growth laws for male versus female names, attributable to different rates of innovation, whereas names from the bible enjoy a genuine advantage at all frequencies. Frequency dependence emerges from a host of underlying social and cultural mechanisms, including a preference for novelty that recapitulates fashion trends in dog owners. Studying culture through the lens of evolutionary theory provides a quantitative account of social pressures to conform or to be different; and it provides inference tools that may be used in biology as genetic and phenotypic time series are increasingly available.

Venue: Okochi Hall (Main Venue) / via Zoom

Event Official Language: English

Higher Gauge Structures and Invariant Action Principles

January 6 (Tue) 15:15 - 16:15, 2026

Sebastián Salgado (External Researcher, Instituto de Alta Investigacion, Universidad de Tarapaca, Chile)

I present the systematic construction of gauge theories based on free differential and L-infinity algebras. This provides a consistent algebraic framework for constructing gauge-invariant theories whose field content is extended by higher-degree differential forms as gauge potentials. I derive explicit expressions for the corresponding extended Chern-Simons actions and the generalized anomaly terms that emerge from them. Possible applications to gravity and supergravity will also be discussed.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Invitation to Random Tensor Models: from random geometry, enumeration of tensor invariants, to characteristic polynomials

January 6 (Tue) 13:30 - 14:30, 2026

Reiko Toriumi (Associate Professor, Okinawa Institute of Science and Technology Graduate University (OIST))

I will introduce random tensor models by first reviewing their motivation coming from random geometric approach to quantum gravity. Then, I will selectively present some of the interesting research results, by highlighting recent results on enumeration of graphs representing tensor invariants, and reporting our recent work on a new notion of characteristic polynomials for tensors via Grassmann integrals and distributions of roots of random tensors. The latter two are based on arXiv:2404.16404[hep-th] and arXiv:2510.04068[math-ph]

Venue: #359, 3F, Main Research Building (Main Venue) / via Zoom

Event Official Language: English

Cosmological correlators beyond the de-Sitter invariance

December 24 (Wed) 15:00 - 17:00, 2025

Zhu Yuhang (Postdoctoral Researcher, Particle Theory and Cosmology Group, Center for Theoretical Physics of the Universe (CTPU), Institute for Basic Science (IBS), Republic of Korea)

Cosmological correlators serve as powerful probes of the physics that governed the Universe in its earliest moments. Yet analytic calculations of correlators involving massive spinning fields are highly challenging. Recent progress in the cosmological bootstrap program has greatly deepened our understanding of these correlators. In this talk, we will show how to extend the bootstrap program beyond exact de Sitter invariance by studying two types of symmetry breaking: explicit scale-invariance breaking and boost breaking. We will present the boundary differential equations that characterise correlators in these settings and highlight the rich phenomenology that emerges. Finally, we will also show recent developments in approximation methods, based on the combination of exact WKB and saddle-point method, which provide a precise, efficient, and physically transparent way to capture and classify the non-analytic features of correlators.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

Origin and evolutionary history of an urban underground mosquito

December 18 (Thu) 13:00 - 14:00, 2025

Yuki Haba (Postdoc, Zuckerman Institute, Columbia University, USA)

Urbanization is rapidly reshaping landscapes around the world, which poses questions about whether and how quickly animals and plants can adapt. Culex pipiens form molestus, more commonly known as the "London Underground mosquito," has been held up as a benchmark for the potential speed and complexity of urban adaptation. This intraspecific lineage within Cx. pipiens, a major West Nile virus vector, is purported to have evolved human biting and a suite of other human-adaptive behaviors in the subways and cellars of northern Europe within the past 200 years. Form molestus features prominently in textbooks as well as scholarly reviews of urban adaptation. Yet, the hypothesis of in situ urban evolution has never been rigorously tested. I will talk our recent efforts to understand the contentious origin and evolutionary history of the urban, human-biting mosquito. Our synthesis and meta-analysis of rich yet confusing literature show that its London Underground origin is unlikely (Haba and McBride 2022 Current Biology). Whole genome resequencing and population genomics of 800+ mosquitoes across ~50 countries again debunk the in situ evolution hypothesis and instead support that molestus first adapted to human environments >1000 years ago in the Mediterranean or Middle East, most likely in ancient Egypt or another early agricultural society (Haba et al. 2025 Science). I will outline implications of our results in urban evolutionary biology as well as in public health. Speaker Bio Yuki Haba, Ph.D., is an evolutionary biologist passionate about understanding how and why diverse behaviors evolve in nature. He is currently a Leon Levy Scholar in Neuroscience at Columbia University's Zuckerman Mind Brain Behavior Institute. He aims to take multi-desciplinary approaches, combining genomics, neuroscience, and field-based behavioral ecology to comprehensively understand the evolution of behavior. Yuki completed his PhD at Princeton, MA at Columbia, and undergraduate degree at the University of Tokyo. Personal webpage: https://yukihaba.github.io/

Venue: Seminar Room #359

Event Official Language: English

Is the Fornax galaxy cluster hiding its radio sources?

December 15 (Mon) 14:00 - 15:15, 2025

Alvina Yee Lian On (PD, Physics Division, National Center for Theoretical Sciences, Taiwan)

Recently, the ASKAP POSSUM and MeerKAT surveys revealed an apparent lack of radio source counts in the Fornax galaxy cluster field. The sources in this patch of sky also appeared to be less polarised. These observations are peculiar and could be important signatures of depolarisation on megaparsec scales. In this talk, I will present some of our recent results, where we quantified the effects on polarisation of radio point sources behind a merging galaxy cluster simulation. The merger gives rise to a large-scale intracluster shock, which compresses the gas and aligns the magnetic field along the shock front. The in-falling subcluster also triggers gas sloshing near the cluster center, resulting in the formation of cold fronts. Our ray-tracing calculations revealed that, generally, bright sources do not experience any significant changes in polarisation, whereas faint sources either get severely depolarised or enhanced as their radiation propagates through the intracluster medium. I will highlight the physical conditions under which polarisation may change significantly along the line-of-sight and discuss how these may impact our interpretations of radio observations, particularly with the SKA.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Widespread conservation of genetic effect sizes between human groups across traits

December 12 (Fri) 13:30 - 15:00, 2025

Simon Robert Myers (Professor, University of Oxford, UK)

Understanding genetic differences between populations is essential for avoiding confounding in genome-wide association studies and improving polygenic score (PGS) portability. We developed a statistical pipeline to infer fine-scale Ancestry Components and applied it to UK Biobank data. Ancestry Components identify population structure not captured by widely used principal components, improving stratification correction for geographically correlated traits. To estimate the similarity of genetic effect sizes between groups, we developed ANCHOR, which estimates changes in the predictive power of an existing PGS in distinct local ancestry segments. ANCHOR infers highly similar (estimated correlation 0.98 ± 0.07) effect sizes between UK Biobank participants of African and European ancestry for 47 of 53 quantitative phenotypes, suggesting that gene–environment and gene–gene interactions do not play major roles in poor cross-ancestry PGS transferability for these traits in the United Kingdom, and providing optimism that shared causal mutations operate similarly in different populations.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

Kyoto University MACS Program Study Group RIKEN Visit and Research Exchange Meeting —Discussing the Cutting Edge with RIKEN Researchers—

December 12 (Fri) 12:30 - 15:10, 2025

12:00 – 13:30 Participate in Coffee Meeting 13:30 – 14:10 Ryosuke Iritani (Senior Research Scientist, RIKEN iTHEMS) — Research Keywords: Mathematical Biology, Evolutionary Ecology 14:10 – 14:30 Break 14:30 – 15:10 Okuto Morikawa (Special Postdoctoral Researcher, RIKEN iTHEMS) — Research Keywords: Lattice Field Theory, Conformal Field Theory, Quantum Field Theory, Particle Physics

Venue: #345-347, 3F, Main Research Building

Event Official Language: Japanese

Self-organized mechano-chemical instabilities drive the emergence of tissue morphogenesis in digit organoids

December 11 (Thu) 13:00 - 14:00, 2025

Antoine Diez (Research Scientist, Mathematical Application Research Team, Division of Applied Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Tissue morphogenesis is an emergent phenomenon: macroscopic structures cannot be predicted from a mere list of genes and cells. We examine here how digits arise from a spherical limb bud and present a framework linking microscopic cellular behavior to morphogenesis. To extract digit morphogenesis in vitro, we created a limb-mesenchyme organoid that breaks symmetry and forms digit-like cartilage. Analyzing cell behavior, iterating between experimental evidence and cellular-based models, shows that microscopic mechanisms like differential adhesion between distal and proximal autopod cells, chemotaxis toward Fgf8b, and biased traction can drive tissue-wide deformations by convergent extension that eventually lead to the formation of digit structures. Taking the continuum limit of these microscopic rules yields a modified Cahn–Hilliard equation, that is well known to describe fluid interfaces and so-called fingering instabilities, but that is shown here to recapitulate well organoid morphogenesis. Taken together, this work suggests that the emergence of “fingers” can be explained in a theoretical framework as a type of fingering instability.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

Full exceptional collections on Fano threefolds and the braid group action

December 5 (Fri) 16:00 - 17:30, 2025

Anya Nordskova (Postdoctoral researcher, Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU))

The bounded derived category D^b(X) of coherent sheaves on an algebraic variety X is a powerful tool that encodes a wealth of information about X. In some cases D^b(X) admits a particularly nice description via so-called full exceptional collections, which allow one to view D^b(X) as being glued from the simplest building blocks, each equivalent to the derived category D^b(pt) of a point. In this situation the set of all full exceptional collections admits an action of the braid group. In 1993, Bondal and Polishchuk conjectured that this braid group action is always transitive. After a short historical overview I will sketch the idea behind the proof of Bondal-Polishchuk's conjecture in the case when X is a Fano threefold of Picard rank 1 (e.g. the projective space P^3). This is the first 3-dimensional case where the transitivity of the braid group action has been verified. The talk is based on joint work with Michel Van den Bergh.

Venue: 3F 345-347 Seminar Room, Main Research Building (Main Venue) / via Zoom

Event Official Language: English

About analytic continuation of quantum field theories in non-integer dimensions

December 5 (Fri) 14:00 - 15:30, 2025

Slava Rychkov (Professor, Institut des hautes études scientifiques, France)

Analytic continuation in dimension has been used first as a way to regularize perturbative quantum field theory. But since the work of Wilson and Fisher, quantum field theory in d-dimension has been used more radically, to connect theories living say, in d=4, to theories in d=3 and d=2. Mathematically it's not fully clear what this means. I will give some thoughts about this subject, and I will describe some recent paradoxes which arise when one consider expansion of O(N) models around d=2, based on recent work with Fabiana De Cesare.

Venue: Seminar Room #359 (Main Venue) / via Zoom

Event Official Language: English

The Functional Renormalisation Group: From the physics of strongly correlated systems to generative models

December 5 (Fri) 10:30 - 12:00, 2025

Jan Martin Pawlowski (Professor, Institute for Theoretical Physics, University of Heidelberg, Germany)

In the past decades, the functional renormalisation group (fRG) has matured into a comprehensive approach to strongly-correlated (non-perturbative) systems, covering quantitatively both universal and non-universal phenomena. The fRG also constitutes an ideal approach for unravelling structural aspects of quantum field theories. This is not only interesting for studies in mathematical physics, but also guides systematic diagrammatic expansion schemes. It is also used to set up novel statistical (lattice) approaches to non-perturbative phenomena. In the present talk I survey these advances and illustrate the progress with selected examples ranging from ultracold atoms, QCD and quantum gravity to novel generative architectures for lattice simulations and beyond.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Biological Background of Duplicated Sequence Evolution: A Focus on Gene Conversion

December 4 (Thu) 13:00 - 14:00, 2025

Kenji Okubo (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Duplicated sequences—such as gene families, tandem arrays, and segmental duplications—are common in many genomes. Their evolution is shaped by several biological processes, including mutation, recombination, duplication, deletion, and gene conversion. Among these, gene conversion is especially important because it can make nearby copies more similar, while leaving distant copies free to diverge. In this seminar, I will give a broad and accessible overview of the biological background related to duplicated sequences, with a particular focus on what is known about gene conversion. I will summarize well-established patterns such as its dependence on genomic distance, sequence similarity, and recombination context. These biological features are often studied separately, so organizing them in one place can help provide a clearer foundation. The goal of the talk is to outline the biological principles that motivate thinking about duplicated sequences in a more formal or quantitative way in the future. I will not discuss specific model details. Instead, this presentation will serve as background preparation for later theoretical work.

Venue: via Zoom / Seminar Room #359

Event Official Language: English

From phase reduction to hypergraphs: the higher-order dynamics of coupled phase oscillators

November 27 (Thu) 13:00 - 14:00, 2025

Riccardo Muolo (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))

Networks are powerful tools in the modeling of complex systems, but they do not always capture the right interactions when multiple units are involved simultaneously. Such many-body interactions are encoded by higher-order structures which can be thought as extensions of networks. Over the last years, higher-order networks have been the focus of great excitement, since this novel framework has enormous potential for applications. In this talk, I will give an overview of higher-order interactions and their effects on nonlinear dynamics. I will introduce the basics of dynamics on networks and its extension to the case of higher-order interactions. As examples of the effects on nonlinear dynamics, I will discuss the case of phase reduction for systems with higher-order interactions and show the effects on synchronization dynamics.

Venue: Seminar Room #359 / via Zoom

Event Official Language: English

Adaptive navigation strategies in adversarial predator-prey contexts

November 20 (Thu) 13:00 - 14:00, 2025

Nozomi Nishiumi (Specially Appointed Associate Professor, Academic Assembly Institute of Science and Technology, Niigata University)

Animal navigation has long been a central topic in behavioral biology. In predator-prey systems, both predators and prey must navigate strategically - predators to capture prey and prey to reach safety - each evolving to outsmart the other through coevolution. To uncover the essence of these navigation strategies, I have investigated behavioral mechanisms across taxa. In bats, my collaborators and I found that they integrate multiple sensory and flight tactics to keep erratically flying moths within detection range. In pigeons, we discovered that individuals anticipating drone attacks adjust their positions toward the rear within the flock. I will also introduce an experimental framework that enables controlled interactions between real animals and virtual agents driven by reactive motion control, allowing quantitative tests of navigation efficiency. Through this seminar, I aim to highlight how studies of predator-prey navigation can bridge biology and engineering, providing insights into adaptive decision-making in dynamic environments.

Venue: Seminar Room #359, Seminar Room #359 / via Zoom

Event Official Language: English

9th QGG Intensive Lectures – Correlation Effects in Quantum Many-Body Systems: Some Prototypical Examples in Condensed Matter Physics

November 19 (Wed) - 20 (Thu) 2025

Norio Kawakami (Deputy Director, Fundamental Quantum Science Program, TRIP Headquarters, RIKEN)

The ninth installment of the Intensive Lecture Series, organized by the Quantum Gravity Gatherings (QGG) study group at RIKEN iTHEMS, will feature Prof. Norio Kawakami from the Fundamental Quantum Science Program (FQSP) under RIKEN's Transformative Research Innovative Platform (TRIP). Over the course of two days, Prof. Kawakami will deliver a lecture series on quantum many-body systems. In recent years, insights from quantum many-body physics have become central to research in quantum gravity, where correlation effects induced by gravity play nontrivial roles. By bridging perspectives from gravitational physics and quantum many-body dynamics, one hopes to understand how macroscopic spacetime and its geometric properties emerge from the collective behavior of quantum constituents at microscopic scales. In this lecture series, Prof. Kawakami will introduce the fundamental properties of correlation effects through representative examples in condensed matter physics. A distinctive aspect of this event is its joint organization with the Fundamental Quantum Science Program (FQSP) at RIKEN. The goal is to further strengthen connections between the quantum gravity, condensed matter, and quantum information communities. The lectures will be delivered in a blackboard-style format (in English), designed to foster interaction, active participation, and in-depth Q&A discussions. In addition, short talk sessions will be held, giving participants the opportunity to present briefly on topics of their choice. Through this informal and dynamic setting, we hope to spark active interactions among participants and create an environment where ideas can be shared openly and enthusiastically. Abstract: Some examples of theoretical methods to treat strongly correlated systems in condensed matter physics are explained. We start with the Kondo effect, which is one of the most fundamental quantum many-body problems and has been intensively studied to date in a wide variety of topics such as dilute magnetic alloys, heavy fermion systems, quantum dot systems, etc. Dynamical mean-field theory (DMFT) is then introduced, which enables us to systematically treat strongly correlated materials such as a Mott insulator. It is shown that the essence of DMFT is closely related to the Kondo effect. Furthermore, we explain how to apply conformal field theory (CFT) to treat correlation effects in one-dimensional electron systems.

Venue: #435-437, 4F, Main Research Building

Event Official Language: English

Contribution of star-forming galaxies to the cosmic gamma-ray background

November 14 (Fri) 14:00 - 15:15, 2025

Junling Chen (Ph.D. Student, Graduate School of Mathematical Sciences, The University of Tokyo)

Fermi Gamma-Ray Space Telescope has measured the diffuse extragalactic gamma-ray background (EGB) radiation in the energy range of 100 MeV to 820 GeV. Several candidate γ -ray sources have been proposed as the candidate components of the unresolved EGB, including active galactic nuclei (AGNs), millisecond pulsars, dark matter annihilation, and star-forming galaxies (SFGs), but their quantitative contribution has not yet been precisely determined. In this talk, I will introduce our latest physical model describing the gamma-ray emission mechanism from SFGs, and our estimate of the contribution of SFGs based on careful calibration with gamma-ray luminosities of nearby galaxies and physical quantities (star formation rate, stellar mass, and size) of galaxies observed by high-redshift galaxy surveys.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English

Topological physics and its interdisciplinary influence

November 12 (Wed) 13:00 - 14:00, 2025

Tomoki Ozawa (Professor, Advanced Institute for Materials Research (AIMR), Tohoku University)

Topological insulators are materials which do not conduct current inside but do conduct at the surface or the edge. The name "topological" comes from the fact that the "shape" of the wavefunction of electrons in topological insulators show non-trivial twist, which can be mathematically characterized by the language of topology. Alongside the development of the study of topological insulators in solids, analogous phenomena were found to exist also in other systems such as photonics, mechanics, geophysics, and active matter. In this seminar, I discuss how the underlying concept of "topology of states" can have a broad impact applicable to various areas in physics, with some emphasis on my own contribution to the field. I aim to structure the first half of my seminar to be accessible to those outside physics, and latter half to be more specialized, covering cutting-edge results.

Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359

Event Official Language: English